The U.S. and Russia agreed on Friday to establish a cease-fire in southern Syria, U.S. Secretary of State Rex Tillerson announced at the G20 summit in Hamburg, Germany. The cease-fire, which begins Sunday at noon local time, marks the nations’ first joint effort under the Trump administration to curb the violence in Syria’s ongoing, six-year civil war. Tillerson said President Trump and Russian President Vladimir Putin reached the “defined agreement” during a lengthy two-hour conversation for which both he and Russian Foreign Minister Sergey Lavrov were present.

On Friday, Lavrov confirmed that Jordan is party to the deal as well. The Associated Press has since reported that Israel is also involved, citing information from a U.S. official. Both Jordan and Israel share a border with southern Syria, giving them a vested interest in mitigating the conflict, as well as strategic access to the region. While many details of the new agreement, including its end date, have yet to be decided, Lavrov said the Russian military would be initially responsible for securing the Daraa, Quneitra, and Suwayda regions in southern Syria. Each nation was also expected to provide humanitarian aid.

While the agreement is a major step forward for U.S.-Russian diplomacy, previous cease-fires have done little to mitigate the violence in Syria. Since 2011, the nation has been embroiled in a massive civil war between the Syrian army, led by President Bashar al-Assad, and various rebel groups who oppose the Assad regime. The conflict has ultimately led to a global refugee crisis and the deaths of around half a million civilians. Since the start of the civil war, both sides have repeatedlyviolated cease-fire arrangements—sometimes within hours of the deals taking effect.

Before Friday, the most recent cease-fire agreement was established in May, when Russia, Iran, and Turkey enacted four safe zones across north, central, and southern Syria. By the following month, the Syrian Network for Human Rights, a U.K.-based war monitor, had documented 75 violations of the agreement—the majority of which were carried out by the Assad regime and its allied forces. Earlier this week, a series of peace talks in the Kazakh capital of Astana failed to produce an agreement between Russia, Iran, and Turkey over which forces would police the zones. Ahead of the peace talks, the Assad regime agreed to halt its combat operations in southern Syria until Saturday—the day before the newest cease-fire is scheduled to begin.

While Russia and Iran are closely allied with Assad, the U.S. and Turkey are key supporters of the Syrian opposition. In the past, the U.S. has refrained from military intervention in the conflict, preferring instead to arm moderate rebel groups and collaborate with Russia to destroy Syria’s chemical-weapons stockpile. Under the Trump administration, the nation has intensified its military targets on Assad, whom the government accuses of attacking innocent civilians using chemical weapons.

In April, the U.S. accused Assad of carrying out a chemical attack on Syria’s northwestern Idlib province, which killed more than 80 civilians, including children. Days after the attack, Trump ordered the launch of 59 tomahawk missiles at a Syrian air base, signifying the nation’s first military operation against an Arab government since 2011. Russia later referred to the U.S. strike as a “provocation” that could damage U.S.-Russian ties. By May, however, the warning seemed to fade, with Putin claiming that U.S. participation in the Syrian conflict was critical to achieving lasting peace.

While Trump and Putin have hinted at their mutual desire to achieve a cease-fire in the region, Tillerson said Friday’s agreement was the “first indication of the U.S. and Russia being able to work together in Syria.” Without offering further detail, he also seemed to simply that Russia might be open to a new era of Syrian leadership. “How Assad leaves is yet to be determined,” he told reporters, while insisting that the U.S. sees “no long-term role” for the regime. “We have made this clear to everyone,” he added. “We certainly made it clear in our discussions with Russia.”

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Aria Bendix is a frequent contributor to The Atlantic, and a former editorial fellow at CityLab. Her work has appeared on Bustle and The Harvard Crimson.